[PATCH 15/17]DVB:Siano drivers - Bug fix - avoid (rare) dead locks causing the driver to hang when module removed.

[Doron Cohen <doronc@siano-ms.com>]

Hi,
This patch step is a  Bug fix - avoid (rare) dead locks causing the
driver to hang when module removed.
Thanks,
Doron Cohen

-----------------------

>From ad75d9ce48d440c6db6c5147530f1e23de2fcb28 Mon Sep 17 00:00:00 2001
From: Doron Cohen <doronc@siano-ms.com>
Date: Tue, 20 Sep 2011 08:46:52 +0300
Subject: [PATCH 19/21] Bug fix - waiting for free buffers might have
caused dead locks. Mechanism changed so locks are released around each
wait.

---
 drivers/media/dvb/siano/smscoreapi.c |   53
+++++++++++++++++++++++++++------
 1 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/drivers/media/dvb/siano/smscoreapi.c
b/drivers/media/dvb/siano/smscoreapi.c
index bb92351..0555a38 100644
--- a/drivers/media/dvb/siano/smscoreapi.c
+++ b/drivers/media/dvb/siano/smscoreapi.c
@@ -1543,26 +1543,59 @@ EXPORT_SYMBOL_GPL(smscore_onresponse);
  *
  * @return pointer to descriptor on success, NULL on error.
  */
-
-struct smscore_buffer_t *get_entry(struct smscore_device_t *coredev)
+struct smscore_buffer_t *smscore_getbuffer(struct smscore_device_t
*coredev)
 {
 	struct smscore_buffer_t *cb = NULL;
 	unsigned long flags;
 
+	DEFINE_WAIT(wait);
+
+	spin_lock_irqsave(&coredev->bufferslock, flags);
+
+	/* set the current process state to interruptible sleep
+	 * in case schedule() will be called, this process will go to sleep 
+	 * and woken up only when a new buffer is available (see
smscore_putbuffer)
+	 */
+	prepare_to_wait(&coredev->buffer_mng_waitq, &wait,
TASK_INTERRUPTIBLE);
+
+	if (list_empty(&coredev->buffers)) {
+		sms_debug("no avaliable common buffer, need to schedule");
+
+		/* 
+         * before going to sleep, release the lock 
+         */
+		spin_unlock_irqrestore(&coredev->bufferslock, flags);
+
+		schedule();
+
+		sms_debug("wake up after schedule()");
+
+		/* 
+         * acquire the lock again 
+         */
 	spin_lock_irqsave(&coredev->bufferslock, flags);
-	if (!list_empty(&coredev->buffers)) {
-		cb = (struct smscore_buffer_t *) coredev->buffers.next;
-		list_del(&cb->entry);
 	}
+
+	/* 
+         * in case that schedule() was skipped, set the process state
to running
+	 */
+	finish_wait(&coredev->buffer_mng_waitq, &wait);
+
+	/* 
+         * verify that the list is not empty, since it might have been 
+	 * emptied during the sleep
+	 * comment : this sitation can be avoided using
spin_unlock_irqrestore_exclusive	
+	 */	
+	if (list_empty(&coredev->buffers)) {
+		sms_err("failed to allocate buffer, returning NULL");
 	spin_unlock_irqrestore(&coredev->bufferslock, flags);
-	return cb;
+		return NULL;
 }
 
-struct smscore_buffer_t *smscore_getbuffer(struct smscore_device_t
*coredev)
-{
-	struct smscore_buffer_t *cb = NULL;
+	cb = (struct smscore_buffer_t *) coredev->buffers.next;
+	list_del(&cb->entry);
 
-	wait_event(coredev->buffer_mng_waitq, (cb = get_entry(coredev)));
+	spin_unlock_irqrestore(&coredev->bufferslock, flags);
 
 	return cb;
 }
-- 
1.7.4.1